1. Field of the Invention
The present invention relates to a transformer and more particularly to a transformer and a transformer assembly that use copper sheets as a primary winding or a secondary winding and is capable of reducing leakage inductance.
2. Description of the Related Art
A transformer is an electromagnetic device that has a primary winding and a secondary winding to convert electrical energy, transfer electrical energy from one circuit to another circuit and is often mounted on a circuit board. Each winding of most conventional transformers has a wire wound in loops. With reference to FIGS. 7 and 8, another conventional transformer substitutes multiple copper sheets for the wire in the primary winding or the secondary winding and has a bobbin (70), multiple copper sheets (80), a coil assembly and a magnetic core (72).
The bobbin (70) is mounted on a circuit board (90) and comprises two side plates and a hollow winding core (71) mounted between the two side plates. The circuit board (90) has multiple printed circuit lines.
Each of the copper sheets (80) is a U-shaped plate with an inner edge and two ends. When each of the copper sheets (80) is mounted on the winding core (71) the inner edge abuts the surface of the winding core (71). The two ends of each copper sheet (80) are connected to the printed circuit lines on the circuit board (90) to form multiple loops in an electrical path through the copper sheets (80).
The coil assembly is wound around the winding core (71) and has two ends being connected to the printed circuit board (90). The magnetic core (72) is mounted through and around the bobbin (70), wherein the broken lines shown on FIG. 8 is for the purpose of indicating an approximate position where the magnetic core is mounted.
However, the transformer constructed by the copper sheets still has some drawbacks.
1. Even though the copper sheets (80) are used to replace the wire in either the primary winding or the secondary winding, a wire wound in loops as the secondary winding or the primary winding is required. However, the transformer does not provide any engaging or positioning means for steadily holding the copper sheet (80) on the winding core (71). When the wire is wound around the winding core (71), some of the copper sheets (80) may be easily moved, which results in the ends of the copper sheets (80) moving. Since the ends of the copper sheets (80) are shifted, soldering the ends of the copper sheets (80) to the printed circuit lines on the printed circuit board (90) will be more difficult.
2. Since the copper sheets (80) are electrically and sequentially connected by printed circuit lines of the circuit board (90), a current (I) flowing from one end of the copper sheet (80) to other copper sheets (80) has to pass through the printed circuit lines. A large gap exists between the winding core (71) and the circuit board (90), the air of the gap results in an imperfect coupling. Due to the imperfect coupling, a high leakage inductance will occur and reduce energy transfer efficiency of the transformer.
To overcome the shortcomings, the present invention provides a transformer to mitigate or obviate the aforementioned problems.